Channel maintenance Dredging at Cabbage Tree Point
Overview of Project
The Gold Coast Waterways Authority contracted Neumann Dredging to undertake maintenance dredging in the Main Channel North at Cabbage Tree Point.
Dredging the channel to -2.7 m, LAT required the removal of over 15,000m3 of sand. The dredging team placed the sand on the foreshore at Cabbage Tree Point, adjacent to the channel.
Significant sand deposition and shoaling within the Main Channel North necessitated dredging to maintain safe navigable depth. This channel forms the primary movement channel for vessels travelling between Moreton Bay’s northern and southern areas. Therefore, it is vital to maintain navigable depths under all tidal conditions. The build-up of sand reduced water depths within the defined navigation channel at low tide to under one metre in some areas. Beach nourishment for recreational amenity was the selected dredge material management option to improve the amenity of the foreshore and provide additional protection to the land, which has been subject to steady erosion.
Scope of Works
- The mobilisation of a 250mm cutter suction dredge, the Nu Discovery, and 500m of 250mm poly pipeline.
- Dredging of 15,000m3 of marine sediments for the main channel.
- Pumping the sediment through the pipeline to the deposition site adjacent to the channel.
Challenges
- Strict environmental guidelines.
- Maintaining suitable access through the channel and maintaining access to the busy boat ramp.
Nu Discovery CSD Used for this Project
The Nu Discovery is a 250mm cutter suction dredge from the Nu Explorer series of dredges. The Nu Explorer series of dredges have been designed and constructed by Neumann Contractors to specifically suit the typical dredging conditions encountered in projects like the Corrie Channel. There are three dredges in the Nu Explorer series that currently complement our fleet (a total of 9 Cutter Suction Dredges):
- Nu Explorer(original dredge in the Nu Explorer Series) has been working in the OTML Mine in PNG for the last two years,
- Nu Discovery has recently completed work in the Iluka Boat Harbour and Entrance Channel Dredging project,
- Nu Investigator is the latest vessel in the fleet and has just completed initial trials and testing at Neumann Contractors, Corridor Sands plant at Woongoolba.
The Nu Discovery is a 227kW (305hp) 250mm three-wire cutter suction dredge. The dredge can dredge up to 120m3 per hour (in optimal conditions), dredge to a maximum depth of 6.5 metres, and pump the material up to 1,000m in the distance.
A three-wire anchoring system manoeuvres the Nu Discovery cutter suction dredge so the dredge operator can set it up to cut the entire channel width, including any batters in just one cut width. The side anchor ropes remain on the sea bed while the dredge is in operation, which will minimise any inconvenience to other boating traffic through the affected channel areas. In addition, the dredge can quickly move to one side of the channel to allow for vessel movements.
